In recent years, intense studies have been conducted on low operating-temperature solid oxide fuel cells to reduce operating temperatures of solid oxide fuel cells to around 600° C. to 800° C. As a solid electrolyte material for low operating-temperature solid oxide fuel cells, lanthanum-gallate-based oxide have been proposed (see, for example, Japanese Patent Application Publication No. 2002-15756 (pages 1 to 9, FIGS. 1 to 9), and Japanese Patent Application Publication No. Hei 11-335164 (pages 1 to 12, FIGS. 1 to 12)). In solid oxide fuel cells in which lanthanum-gallate-based oxide is used as a solid electrolyte material, NiO—YSZ having similar thermal expansion properties is employed as a support material. Nevertheless, NiO—YSZ is expensive, and hence an inexpensive support material is desired. In this regard, the use of relatively inexpensive forsterite-based sintered compact as a support material has been proposed (see Japanese Patent Application Publication No, 2005-93241).